Mechanics of randomly packed filaments—The “bird nest” as meta-material

Weiner, Nicholas; Bhosale, Yashraj; Gazzola, Mattia; King, Hunter

doi:10.1063/1.5132809

Cited by 45 publications

(36 citation statements)

References 94 publications

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“… 55 , 56 This mechanism of load transfer has been observed in systems across a variety of length scales including bird nests, bamboo skewers, and colloidal gels. 57 − 59 As the number of contacts between rigid rods increases with increased misorientation, 60 it is expected that jamming occurs more frequently in the less aligned INT fibers and leads to more efficient stress transfer within the fiber and hence a higher modulus. The deformation of these fibers may be considered as analogous to the shear of granular assemblies of frictional rigid rods.…”

Section: Mechanical Properties Of Dw Ge-int Fibersmentioning

confidence: 99%

Continuous Binder-Free Fibers of Pure Imogolite Nanotubes

Moore

Paineau

Launois

et al. 2021

ACS Appl. Mater. Interfaces

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Imogolite nanotubes (INTs) display a range of useful properties and provide an ideal material system to study the assembly of nanomaterials into macroscopic fibers. A method of wet spinning pure, binder-free imogolite fibers has been developed using double-walled germanium imogolite nanotubes. The nanotube aspect ratio can be controlled during the initial synthesis and is critical to the spinning process. Fibers made from short nanotubes (<100 nm) have very low gel strengths, while dopes with longer nanotubes (500–1000 nm) are readily spinnable. The tensile behavior of the resulting imogolite nanotube fibers is strongly influenced by relative humidity (RH), with a modulus of 30 GPa at 10% RH compared to 2.8 GPa at 85% RH, as well as a change in failure mode. This result highlights the importance of inter-nanotube interactions in such assemblies and provides a useful strategy for further exploration. Interestingly, in the absence of a matrix phase, a degree of misorientation appears to improve load transfer between the individual INTs within the porous fiber, likely due to an increase in the number of interparticle contacts. Imogolite nanotubes are an appealing analogue to other nanotube fiber systems, and it is hoped that learnings from this system can also be used to improve carbon nanotube fibers.

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Section: Mechanical Properties Of Dw Ge-int Fibersmentioning

confidence: 99%

Continuous Binder-Free Fibers of Pure Imogolite Nanotubes

Moore

Paineau

Launois

et al. 2021

ACS Appl. Mater. Interfaces

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“…Interlocking geometries can be utilized to create kinematic constraints to only allow for motion in particular directions. [ 31–35,53–57 ] Fibers can have prismatic cross sections, rather than circular ones to avoid kinematic rearrangement in particular directions and to transform the contact lines between constituents into contact surfaces. [ 14 ] Particles can be designed with particular geometries to create larger number of contact points, or larger contact surface areas between the particles.…”

Section: Resultsmentioning

confidence: 99%

A Modeling Framework for Jamming Structures

Aktaş

Narang

Vasios

et al. 2021

Adv Funct Materials

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Jamming is a structural phenomenon that provides tunable mechanical behavior. A jamming structure typically consists of a collection of elements with low effective stiffness and damping. When a pressure gradient, such as vacuum, is applied, kinematic and frictional coupling increase, resulting in dramatically altered mechanical properties. Engineers have used jamming to build devices from tunable‐stiffness grippers to tunable‐damping landing gear. This study presents a rigorous framework that systematically guides the design of jamming structures for target applications. The force‐deflection behavior of major types of jamming structures (i.e., grain, fiber, and layer) in fundamental loading conditions (e.g., tension, shear, and bending) is compared. High‐performing pairs (e.g., grains in compression, layers in shear, and bending) are identified. Parameters that go into designing, fabricating, and actuating a jamming structure (e.g., scale, material, geometry, and actuator) are described, along with their effects on functional metrics. Two key methods to expand on the design space of jamming structures are introduced: using structural design to achieve effective tunable‐impedance behavior in specific loading directions, and creating hybrid jamming structures to utilize the advantages of different types of jamming. Collectively, this study elaborates and extends the jamming design space, providing a conceptual modeling framework for jamming‐based structures.

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“…Many bird species rely on no other ingredients than the elasticity of sticks and the frictional contacts between them to build their nests [1]. Most of bird nests can be seen as networks of randomly packed entangled fibres which conform mechanically stable structures that are capable of bear the weight of the bird and its eggs.…”

Section: Introductionmentioning

confidence: 99%

Cohesion of bird nests

et al. 2021

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One striking difference between aggregates of flexible frictional fibres and other granular materials like rigid spheres is the effective cohesion of their assembly. While glue or capillary bridges are needed to shape aggregates of spherical particles and build sandcastles, for fibres, no need for glue to build a nest. Here we study an assembly of mono disperse flexible fibres. We first use X-ray microtomography to characterise the geometry of the initial assembly, the number of contact points and mean curvatures of the fibres. Using forcedisplacement measurements, we characterise the macroscopic cohesive strength of the aggregate by varying the geometry of the fibres, the fibres mechanicals properties and the packing of the preparation. Finally, we relate the macroscopic mechanical behaviour of the assembly with the filament reorganisation at the microscopic scale.

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Mechanics of randomly packed filaments—The “bird nest” as meta-material

Cited by 45 publications

References 94 publications

Continuous Binder-Free Fibers of Pure Imogolite Nanotubes

Continuous Binder-Free Fibers of Pure Imogolite Nanotubes

A Modeling Framework for Jamming Structures

Cohesion of bird nests

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